This invention relates generally to a ferromagnetic resonance probe and method for testing for surface flaws in metals.
The traditional approach to eddy current testing for flaws in metals uses a small search coil to induce eddy currents in the metal surface being examined. Flaws are detected by observing changes in the input impedance of the search coil or by observing the frequency shift of a resonant circuit including the coil.
A microwave variant of the resonant circuit approach is to induce eddy currents in the test sample by fields fringing through a small aperture in the wall of a microwave cavity. The presence of flaws perturbs the resonant frequency of the cavity through interaction with the fringing fields. Spatial resolution is determined by the size of the aperture.